Especially when drawing a long pattern from the sand, getting the pattern to draw out of the sand without bumping the sand can be challenging. I commonly have to draw 30 and 36” long patterns freehand from a mold. Avoiding accidentally traversing left, right, fore and aft, rotating about a vertical axis and finally not tilting around a horizontal axis all have to be done to get a clean draw. One thing I recently learned that has helped a lot is to make a small pen mark on the middle of the pattern on the edge near me and make a scratch in the sand next to the pattern mark. Now as I withdraw the pattern I can use the mark to observe for left, right, for, aft and rotational deviations keeping my eyes on that mark alone. I don’t have to try to scan to each end of the,pattern and then back to the near edge. What I am trying to express here may be unclear, but it is a technique that helps me and might be worth a try. It does not help much with rotation around a horizontal axis, but I can pretty much feel those through angular deviation of the draw spike. One more thing it took me too long to learn is a tweak of my initial popping the pattern loose from the sand. I used to put gentle up traction on the left spike rap upward on the left hand spike until I could see the pattern start to free itself and maybe rise an 1/8th of an inch or so and the move my attention and rapping to the right pattern end. BUT, pulling rapping up on the right would almost invariably cause the left end to descend back into the sand. So, back to the left and pop maybe a quarter and then back to the right. Uggh. That potentially caused some degradation of fine details like lettering. So, wonder of wonders, I found that maintaining gentle upward traction on the left spike and rapping up on the right prevented settling on the left. That resulted in a cleaner draw. Maybe very one else already does it that way. But,this is an improvement for me. FWIW. Denis
I'm using some 3/8" x 12" long pins on the cope and drag to give some guidance on that recent project of mine but it's too easy to get cocked over and jam if you're not careful, maybe some sacrificial nylon bushes would help.
This is one of the areas that hobbiest get to ignore "most the time" Flasks need pins that run about 3/4 of to the full height of the Cope , if you are using cheeks, even as upsets you are PROBABLY going to need to use loose pins, in the picture below, the pin is just a precision ground 1/2 inch (probably hardened and chromed) loose pin that extends entirely through the flask and acts well, as a Guide pin for the entire distance of the pull , (pin is not shown you will have to visualize) Hobbiest normally don't get into this sort of thing, because we simply cannot lift this much sand alone , Notice no trunnions, so the pictured flask are probably being hand lifted by a manly molder V/r HT1
I agree with the issue of long pins tending to lock up. However I found that elongating one of the two holes that the pins pass through can help alleviate that problem. So, I have the number one pin passing through a hole that is maybe .005" oversize in diameter and the number two pin hole is .005 over pin size in width but maybe .060 over length. So, pin one really contols position in the x and y-axis on one end of the mold and pin two makes sure its end lines up in the y-direction since pin one is already controling the x-alignment. But the elongation of the number two holes allows some cocking of the mold while not causing locking. Also making sure the guide holes are thin at point of contact is important. Cocking will lock a pin passing through a 1/2" tall cylinder even if it is the sole guide pin. But a grommet-shaped hole allows a lot of cocking without binding. I know it is traditional to have the pins and holes located on the ends of the molds, but for long molds I much prefer them on side near me. That way I can get visual clues with respect to cocking and rotation in the x-y plane as I mate the cope onto the drag. Might be something to try if you haven't already. Denis
That's some food for thought, when you say the hole is elongated, do you mean it's oval in shape?. I had been planning to taper the pins once the cope and drag are separated a few inches and the draft of the pattern gives some clearance... that may make the cocking worse. I see on youtube one foundry had pins with an isoceles triangular cross section maybe that gives some advantage too.
I make two guides. For one I just drill a 1/2" hole in one side of a 1/8 x 1 x 1 angle holding it in my mill vise and then put an end mill in the spindle and move the table a few thou in the x and then y direction to slightly enlarge that hole. To make a second guide I "elongate" the hole by drilling, say, a half inch hole in one face of a piece of 1/8 x 1 x1" angle iron holding that piece in a vise on my mill. Then I replace the drill with a 1/2" end mill and crank the x .030 in each direction and repeat this x excursion after cranking .005 into the y. So now I have a slot .505" wide with round ends and .560 long. I hope that makes sense. So it is not truly an oval as I do not want much slop in the Y direction but I do want a little in the x direction between the two pins. The thinness of the 1/8 angle allows for some rotation about the x axis of the mold and the x tolerance in the one loose guide allows for some rotation around the y axis. Denis
